AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Detailed Characterization of Shape-Selected Fractal Soot Particles
ALLA ZELENYUK, Dan Imre, Josef Beranek, Paul Reitz, Pacific Northwest National Laboratory
Abstract Number: 591 Working Group: Combustion
Abstract Recently we developed a novel system to measure simultaneously individual particles compositions, mass, mobility, and vacuum aerodynamic diameters. In this system, a new-generation compact aerosol particle mass analyzer (APM) is used to generate particles with a narrow distribution of masses that are classified with differential mobility analyzer (DMA) to select particles with one charge and a narrow distribution of mass and shape. The compositions and vacuum aerodynamic size distributions of these particles are measured with single particle mass spectrometer, SPLAT II.
The combined APM/DMA/SPLAT or ADS yields particle size, composition, density/effective density, and dynamic shape factors (DSFs) in the transition and free-molecular regimes.
We applied the ADS to aspherical ammonium sulfate and NaCl particles and demonstrate that both are present in a wide distribution of shapes and that the ADS can be used to select particles of the same volume equivalent diameter, but with very different shapes. For each particle shape, we measure the DSFs in the transition and free-molecular regimes. This approach produces direct relationship between the dynamic shape factors in the two regimes as a function of particle size and makes it possible to separate in real time particles with different shapes for further analysis by SPLAT II or microscopy.
We then apply the ADS to characterize fractal soot particles produced by miniCAST soot generator. We show that in this case it is possible to determine fractal dimension of soot agglomerates, the average primary spherule diameter, number of primary spherules, and void fraction as function of particle size. We show that it is possible to separate soot aggregates of one mass, but with different shapes, and characterize their DSFs in the transition and in the free-molecular regimes. In addition, we demonstrate a new approach to determine the average primary spherule diameter based on the DMA/SPLAT measurements alone.